1. Field of the Invention
The present invention relates to hearing aids and to methods of making hearing aids. The invention more specifically concerns a method for manufacturing a hearing aid component adapted for fitting in the auditory canal of a hearing aid user, said hearing aid component being provided with a resilient material on at least its outside surface, the method comprising acquiring data representing the shape of the auditory canal of a hearing aid user.
2. Prior Art
It is known to manufacture custom fitted ear plugs for hearing aids, or custom fitted in-the-ear hearing aids in hard non-resilient materials. These are typically manufactured by making an impression of the ear, including the auditory canal, of the hearing impaired person. From this impression the ear plug or hearing aid may be manufactured by different techniques. See e.g. WO 02/078233.
When ear plugs are manufactured in resilient material it is known to make a mould directly from the impression of the ear and ear canal. The resilient ear plug is then cast in this mould. It is also known to make an impression in silicone directly from the ear, and then apply this silicone impression with some modifications as an ear plug, e.g. after providing space for arranging the receiver.
One of the more commonly used techniques comprises performing a scanning of the ear impression or a direct scan of the auditory canal in order to obtain data for a three dimensional computer model of the auditory canal. This model can be used when designing e.g. a custom fitted ear plug or a shell for an in-the-ear hearing aid. Such ear plugs or shells can be manufactured by the rapid prototyping processes. In such processes the three dimensional shape of e.g. an ear plug is divided into a number of thin cross-sectional layers (typically about 0.1 mm). The ear plug or hearing aid shell is then built up layer by layer in an additive process. One example of a rapid prototyping process is Stereo Lithography (SLA), where a container of photosensitive resin contains a vertically-moving platform. The ear plug or hearing aid shell under preparation is supported by the platform that moves down by decrements that determine the layer thickness for each layer. A laser beam traces out the shape of the intended specimen in a respective layer to harden the photosensitive resin along the trace. The process repeats until the ear plug or hearing aid shell is complete.
Another example of a rapid prototyping process is Selective Laser Sintering (SLS), where two powder magazines are placed on either side of a work area. A leveling roller moves powder over from one magazine, crossing over the work area to the other magazine. The laser then traces out the shape of the specimen. The work platform moves down by the thickness of one layer and the roller then moves in the opposite direction, thereby moving powder over the work area from a different magazine. Also this process repeats until the ear plug or hearing aid shell is complete.
One problem with rapid prototyping is that this method is only suited for relatively hard and non-resilient materials. The material in which hearing aid components are manufactured by this technique is often acrylic or something with an equivalent hardness. Resilient or soft materials for hearing aid plugs are only known from standard, not custom fitted, ear plugs.
It is known from WO 2007/000160 to shape a tube for conveying sound into a given shape. The tube is shaped by placing it in a tool manufactured using a rapid prototyping process. The tool will form the tube in the preferred shape, and when heating and afterwards cooling the tube this shape is maintained when the tube is removed from the tool.
Often there is a need for custom fitted ear moulds or custom fitted in-the-ear hearing aids with a soft or resilient outer surface, where this surface is intended for contacting the auditory canal. A soft and resilient outer surface of the component of the hearing aid in contact with the auditory canal wall will more easily adapt to the shape of the auditory canal wall, and thereby be more comfortable to the hearing aid user. Furthermore, a soft and resilient outer surface will make continuous adaptation to changes in the geometry of the ear canal feasible. Such changes in geometry may be caused when the hearing aid user is chewing or yawning.
For many users a soft, pliable and resilient ear plug which is custom fitted to the individual shape of the auditory canal will be the optimum solution as this will avoid localized mechanical pressure in the auditory canal. The problem is that this type of ear plugs is relatively time consuming to manufacture with the existing methods, since these methods are more or less manual.